B cells are critical players in the orchestration of properly regulated immune responses that provide protection against infectious agents without inflicting auto-inflammatory damage. Achieving this physiological balance requires the finely regulated participation of multiple B cell populations with different antibody-dependent and independent functions. This is a rather precarious balance since, as demonstrated by multiple studies, since B cells also mediate powerful pro-inflammatory effector functions which if unchecked contribute to the pathogenesis of multiple pathological conditions of great impact in the health of the population including multiple autoimmune conditions, transplant rejection, atherosclerosis, defective cancer surveillance, COPD, asthma and liver fibrosis. The complexity and clinical relevance of B cells has also been brought to the fore in recent years by the success of Rituximab-based B cell depletion therapy (BCDT) in multiple autoimmune diseases. It is therefore apparent that understanding the phenotypic heterogeneity and functional division of labor among different B cell populations will be critical to unravel the pathophysiology of autoimmune diseases and other major clinical conditions. This central goal will be accomplished through the interactive work of 4 projects and two major cores under the administrative oversight provided by Core A;Project 1: Human transitional B cells: homeostasis, function and impact of BCDT;Project 2: Human effector B cells: homeostasis, function and regulation in SLE;Project 3: Evaluation of IFNg-producing effector B cells in infectious and autoimmune disease;Project 4: Role of B cells in Synovial Inflammation and Lymph Node Remodeling in Inflammatory Arthritis;Core B: Coordinating Clinical Core;and Core C: Biostatistics and Data Management Core. The knowledge derived from the work proposed in this PPG should also enable investigators to better design and evaluate vaccine responses. Finally, and central to this PPG, our results will greatly enhance our ability to design better and safer BCDT therapies and to develop biomarkers of B cell targeted treatments efficacy and safety. RELEVANCE: Understanding the proper balance of protective and deleterious B cell functions is of the utmost importance for understanding and treating multiple autoimmune diseases such as Lupus, Rheumatoid Arthritis, Diabetes and Multiple Sclerosis. This knowledge would also greatly help in designing and evaluating vaccines. This PPG brings together a group of talented B cell scientists and clinicians to evaluate in a synergistic and complementary way the identity and function of several new B cell populations and their role in disease using human diseases as well as appropriate animal models for these diseases. PROJECT 1: Title: Human Transitional B Cells: Homeostasis, Function, and Impact of BCDT Project Leader: ANOLIK, J PROJECT 1 DESCRIPTION (provided by applicant): B cells play a critical role in the pathogenesis of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). A major focus of Project I is to define the bone marrow developmental cues and peripheral turnover of transitional B cells and how cytokine milieu, which may be perturbed in systemic autoimmunity, regulates this process. It is hypothesized that autoimmune disease is associated with dysregulation of transitional B cell homeostasis during B cell development with alterations in the numbers of transitional B cells emerging from the bone marrow (BM), the microenvironmental signals that modulate this process (IFN, TNF), and the signaling threshold for progression to the mature compartment (BAFF). On the other hand, we have found that SLE patients with a prominent expansion of circulating transitional cells after B cell depletion therapy (BCDT) enter long-term clinical remission, whereas both SLE and RA patients with more rapid memory reconstitution experience earlier relapse of disease. The focus of this proposal is to understand early B cell homeostasis and the factors that regulate B cell reconstitution after BCDT in SLE and RA through the following specific aims which will define: 1. the perturbations in homeostasis of human transitional B cells in autoimmune disease;2. the factors which regulate the balance of reconstitution of distinct B cell subsets after BCDT;and 3. the reciprocal regulation of transitional B cells and regulatory T cells and how this is altered in autoimmune disease and after BCDT. Specifically, we will define the dynamics of B cell development in humans using B cell depletion as a tool and multi-parameter flow cytometry. The lifespan and turnover of transitional B cells will be assessed by heavy water labeling, replication history, cell cycle, and delineation of survival and selection. The effects of cytokine milieu on new BM B cell lymphopoiesis will be examined. This project will explore the hypothesis that the outcome of BCDT reflects the balance between protective (regulatory, anti-inflammatory) and effector (proinflammatory) B cells and their corresponding cytokines. Transitional B cell functions to delineate include the production of anti-inflammatory cytokines such as IL-10 and TGFB and support of regulatory T cell (Treg) development. We will define whether human B cell subsets differentially support Treg expansion or are differentially susceptible to Treg suppression, if this function changes in autoimmune settings, and how these abnormalities are modified by BCDT. Elucidation of the homeostatic regulation of human transitional B cells will represent a major advance in human B cell biology. The research proposed will also help us understand how B cell development is dysregulated in autoimmune disease and how depletion induces improvement and, in some cases, long-lasting disease remission. RELEVANCE: Lupus and rheumatoid arthritis are chronic autoimmune diseases characterized by an abnormal immune response against self. B cells are a key immune cell in autoimmune disease in part because they play a central role in the production of auto-antibodies, a hallmark of the disease process. This research will help us understand the dysregulation that occurs in B cell development in these diseases and how B cell depletion may induce improvement.